Findings from a new federal study suggest that U.S. schoolchildren may not improve their reading skills until they have a better grasp of basic vocabulary.

The study was released Thursday from the U.S. Department of Education's National Center for Education Statistics, looks at the vocabulary skills of students nationwide and finds that they closely track students' reading comprehension levels.

For fourth-graders, for instance, the top 25% of readers turned in an average 255-point vocabulary score on a 500-point scale; meanwhile, the weakest 25% of readers scored only 177 points.

The findings represent the first time that the federal government has analyzed vocabulary in isolation, and the results show that students have a long way to go: The average fourth-grader scored 218 points in 2011, essentially unchanged from 2009. The average eighth-grader scored 265, also unchanged from 2009. Twelfth-graders' results for 2009 averaged 296 points, but the test wasn't repeated in 2011.

The results come from the biennial National Assessment of Educational Progress (NAEP), commonly called The Nation's Report Card.

Francie Alexander of the children's publishing house Scholastic said the results show that developing a rich vocabulary "can become a huge task for students," one that schools must take on "beginning in the earliest grades and continuing through high school." Alexander is also a former member of the National Assessment Governing Board, which oversees NAEP testing.

While the new effort isn't explicitly tied to more rigorous Common Core standards being piloted in schools nationwide, the new test in a sense closely follows the Common Core's direction. Common Core, which will be in place in most states by 2014, asks teachers to teach fewer subjects with more depth.The NAEP vocabulary test demanded more high-order, abstract thinking from students, inviting them to use the context of a passage to figure out words' meanings instead of simply asking them to define words in isolation.

In a one question, fourth-graders were asked to define the word "puzzled" as used in a reading passage about two boys who visit Boston's Public Gardens, the setting for the classic children's book Make Way for Ducklings. In the passage, the boys are "puzzled" that there are no ducks around.

Asked to pick from four possible definitions, only 51% correctly chose "confused that there were no ducks."

The choices:

a. trying to follow the ducks

b. hoping to play games with the ducks

c. surprised that there were so many ducks

d. confused that there were no ducks

Robert Pondiscio of the Core Knowledge Foundation, a non-profit curriculum advocacy organization based in Charlottesville, Va., said a rich vocabulary is absolutely key to students' academic success - previous research has suggested it's the single biggest indicator of a student's future achievement. "It's kind of the skill of skills," Pondiscio said.

He welcomed the federal government's new focus on vocabulary, but worried that it might lead to teachers simply assigning students to memorize long lists of words. It won't work, he said. "The context is what matters."

Rather, Pondiscio said, schools need to help kids develop bigger vocabularies through reading in a broad variety of topics.

Previous research has shown that low-income children tend to have far smaller vocabularies than their middle-class peers, a deficit that dooms many to an inferior education before it even begins.